WASHINGTON, Sept 5 (Reuters) - An American Airlines mechanic was on Thursday charged with purposely damaging an aircraft in July amid a dispute between the airline and its mechanics union involving stalled contract negotiations.

Pilots of a flight from Miami to Nassau, Bahamas on July 17 aborted take-off plans after receiving an error message involving the flight computer, which reports speed, pitch and other data, according to a criminal complaint filed in U.S. District Court of Southern Florida.

It said after returning to the gate for maintenance, a mechanic discovered a loosely connected pitot tube that measures airspeed and connects directly to the flight computer.

A later review of video surveillance footage before the flight captured "what appears to be the sabotage of the aircraft" by a man walking with a limp, the complaint said.

When suspect Abdul-Majeed Marouf Ahmed Alani was interviewed, he told law enforcement he was upset at the stalled contract between the union and American, which he said had affected him financially, according to the complaint. It said Alani claimed to have tampered with the aircraft to cause a delay or have the flight canceled in anticipation of obtaining overtime work.

Unions have complained that American is trying to outsource more maintenance jobs, a move American has indicated is necessary to cover increased wages.

A U.S. federal court last month issued a permanent injunction against American's mechanics union, which the airline had accused of illegal slowdowns it said had devastated its operations during the peak summer travel season.

A spokesman for American said the airline had an "unwavering commitment" to safety and security and had placed passengers on the July 17 flight subject to the criminal complaint on another plane to get to their destination.

"At the time of the incident, the aircraft was taken out of service, maintenance was performed and after an inspection to ensure it was safe the aircraft was returned to service," the spokesman said. "American immediately notified federal law enforcement who took over the investigation with our full cooperation."

The Miami Herald reported that Alani is set to make an initial court appearance on Friday. Court records did not indicate if Alani had an attorney.

The U.S. federal court order last month prohibits employees from "calling, permitting, instigating, authorizing, encouraging, participating in, approving, or continuing any form of disruption to or interference with American's airline operations," including a refusal to accept overtime or complete any maintenance repairs in the normal course of work.

Reporting by David Shepardson; Additional reporting by Tracy
Rucinski in Chicago; Writing by Jamie Freed; Editing by
Christopher Cushing